Adaptive Cruise Control (ACC) has been available for sales in automobiles for a long time. In fact, as early as the 1910s a centrifugal governor was used in automobiles to control the velocity thereof. Modern ACC systems are configured to control vehicle velocity such that it matches a set speed given by a driver. The ACC systems are normally configured to control the velocity of a vehicle such that a safe distance is maintained to a preceding vehicle. Such control is based on sensor input from on-board sensors such as RADAR (RAdio Detection And Ranging) or LASER (Light Amplification by Stimulated Emission of Radiation) sensors, allowing the vehicle to slow down when approaching another vehicle ahead and accelerate again to the a pre-set speed when traffic allows. ACC system is sometimes regarded as a key component in future generations of cars and has an impact on e.g. driver safety.
However, ACC systems fail to control host vehicle velocity to match a safe and/or pleasant vehicle velocity in many driving situations. As a result, vehicle drivers have to manually control host vehicle velocity in such driving situations. Examples of such driving situations are driving on curved or hilly road, city driving, driving on a road comprising road bumps, roundabouts, intersections, multi-lane highways etc. Ideally, the ACC system should be able to continuously control speed to match a speed which a driver would choose when driving without the ACC system actively controlling the speed.
In a known example, a driver activates the ACC system and sets a following distance to cars preceding a vehicle in which the driver sits. In this example, the driver is able to select from a number of pre-set, or predetermined, following distances. A problem is that the driver tends to change the pre-set following distance for various reasons. Since the driver needs to change the pre-set following distance to another pre-set following distance, the driver may feel that usability of the ACC system is not satisfying.
US2009/0271084 discloses a cruise control system including a traffic condition acquisition unit that acquires a traffic condition that includes a vehicle density on a road on which a vehicle runs. Furthermore, the cruise control system includes a cruise control unit that performs cruise control on the vehicle so that a following distance has a less tendency to decrease as the road gets busier. The following distance refers to distance, measured in terms or meters or seconds, to a vehicle preceding the present vehicle. A problem with the cruise control system may be that the following distance may still not be optimal in some situations. In these situations, a surrounding vehicle is able to cut in in front of the vehicle, since the cruise control system has a less tendency to decrease the following distance as the road gets busier. Consequently, the vehicle may come at a disadvantage with respect to surrounding vehicles which as mentioned cut in in front of the vehicle.